The present invention relates to pumps and motor-pump aggregates in general, and more particularly to improvements in heat barriers for use in motor-pump aggregates or assemblies of the type wherein the pump serves to convey, either continuously or at times, a fluid medium which is maintained at an elevated temperature. Still more particularly, the invention relates to improvements in motor-pump aggregates wherein the heat barrier is disposed between the motor housing and the pump housing and the region between the two housings does not or need not contain any seals for the motor shaft which drives the impeller means of the pump.
The purpose of heat barriers in motor-pump aggregates of the type wherein the pump conveys hot or extremely hot fluids is to prevent the transfer of heat from the pump to the motor. Presently known heat barriers utilize combinations of devices which resort to gaseous and liquid coolants. Such heat barriers are sufficiently effective to insure that the pump can be placed relatively close to the motor, i.e., that the length of the motor shaft can be held to a minimum and that the motor shaft is not likely to wobble. As a rule, the heat barrier between the motor housing and the pump housing comprises a large-diameter flange which is secured to the motor housing and is formed with several large channels for circulation of substantial quantities of a liquid coolant. A drawback of such aggregates is that the manufacturing cost of the heat barriers is very high because they cannot be produced by casting, i.e., they are made in several sections which are welded to each other. The pressure of circulating liquid coolant is relatively low; on the other hand, the pressure in the interior of the motor housing and pump housing is high or extremely high. Consequently, welded connections between the sections of the heat barrier must be very strong and of uniform quality in order to withstand the stresses which arise due to different thermal stressing of different parts of the heat barrier. Therefore, such heat barriers must be inspected at frequent intervals which, in addition to the already high initial cost, contributes to substantial maintenance cost of the aggregate. An additional drawback of liquid-cooled heat barriers is that the entire plant or a large part of the plant must be shut down in the event of failure of the circulating system for the liquid coolant.
It was also proposed to utilize relatively long heat barriers which are cooled exclusively by surrounding air. Such heat barriers are satisfactory only if their length suffices to insure adequate dissipation of heat in the space between the pump housing and motor housing. This, in turn, creates problems in connection with mounting of the shaft which receives torque from or forms part of the motor and transmits torque to rotary parts of the pump. An improperly centered shaft is likely to vibrate and/or to cause vibration of rotary parts of the motor and/or pump. Therefore, the just described air-cooled heat barriers failed to gain widespread acceptance in the industry, i.e., it is normally preferred to resort to liquid-cooled heat barriers.